Earth boring machine



Oct? 22, 1957 M l. COHEN ET EARTH'BORING mcnms' 5 Shets-Sheet 1 FiledApril 1', 1952 N VEN TORS "HR/Q LS/HOBE COHEN 6ND Kan/Aw JAMES cuLp/,g-rTy5 Oct. 22, 1957 M. I. COHEN ETA L ,3 0,

EARTH BORING MACHINE Filed April 1, 1952 5 Sheets-Sheet 2 Q m vz/vrogs NMHEK 100195 COHEN AND RONALD JAMES GULLY meeflm gwda A TTOTclVEYS M. l.COHEN ETAI. 2,810,550

EARTH BORING MACHINE Filed April 1, 1952 5 Shets-Sheet'fi MARK 15/0025COHEN cm RONALD JAMES GULLY ATT" oak/Eva Oct. 22, 1957 Filed April 1,1952 M. I. COHEN ETAL EARTH BORING MACHINE 5 Sheets-Sheet 4 Lyn /'/vvsN-roes RONALD JAMES GULLV fi BNEYS Mme/c 5 0012: 0011mm United StatesPatent p EARTH BORING MACHINE Mark Isidore Cohen, Elwood, nearMelbourne, Victoria, and Ronald James Gully, Maidstone, near Melbourne,Victoria, Australia Application April 1, 1952, Serial No. 279,724

9 Claims. (Cl. 25522) This invention relates to an improved earth boringmachine of the type generally referred to as a post hole digger, and itrefers particularly to a hydraulica1lyoperated machine for boring holes,in the earth, in any type of soil which is relatively rock-free.

In hydraulically-operated post hole diggers as hitherto made it has beenknown to provide a boring bar, usually of rectangular section, attachedto a vertically reciproeating piston, the rectangular bar passingthrough rectangular glands housed in the piston cylinder. In such anarrangement it is technically not possible in practiceespecially owingto wear of the parts which occurs in use-to prevent soil and grit frombeing carried by the boring bar into the interior of the oil-filledcylinder wherein the piston is located. As a result there is causedexcessive wear of the piston and/ or the cylinder, as well as of thepumps and valves, and there is consequently caused leakage of oil due tothat ingress of grit and soil. Moreover, in previously knownconstructions of post hole diggers the boring member has been attacheddirectly to the piston and, therefore, it has been required to passthrough the cylinder wherein the piston is mounted. As a result it hasbeen necessary to restrict the cross-sectional size of the boring bar tothe limits defined by the area of the cylinder.

The principal object of this invention is to provide a construction ofhydraulically-operated post hole digger in which all the oil-operatedcomponents of the machine will be sealed against the ingress of grit andsoil, so that wear of the parts will be greatly reduced. A furtherobject is to devise a construction of apparatus of the type specified,in which the strength of the boring member of the machine may beincreased. Another object is to provide, in a post hole digger, meanswhereby air may be introduced to the bottom portion of a hole bored bythe use of the apparatus so as to facilitate the withdrawal of theauger, and earth carried thereby, from the hole. A dependent object isto devise a construction of air passageway or conduit, for an air bleedto the bottom portion of an auger, which will be of simple character andadapted to be readily incorporated in an earth boring machine. A stillfurther object is to provide a construction of earth borer having simpleyet efficient means whereby an anger may be disengaged from anobstruction in the earth. And yet another object of the invention is toprovide a post hole digger that will be of extremely sturdy design andconstruction, relatively economical to manufacture, and efiicient inoperation.

The invention devised with these and other objects in view consists,broadly, of a post hole digger having a cylinder,-means for driving thecylinder rotationally about its central longitudinal axis, a pistonmounted in the cylinder, means for supplying fluid under pressure asdesired to either one side or the other of the piston so as to move thecylinder linearly in either one direction or the opposite direction, andmeans for attaching a boring member to the cylinder, the piston being soPatented Oct. 22, 1957 mounted that ingress of dust, grit and otherforeign matter to the interior of the cylinder will be prevented.

The boring member consists of or includes an auger and a feature of theinvention resides in the provision of' means for introducing, to thelower end portion of the auger, a supply of air so as to assist in theremoval of the auger from the earth. This may be done by means of aliner tube leading to an air bleed hole at the bottom of the cylinder orby means of an air supply pipe fastened to the outside of the cylinder.In the latter case the air supply pipe may also act as a spline memberfor the transmission of rotary motion to the cylinder.

It is also a feature to mount the auger at the lower end of the cylinderin such a manner that in the event of the auger jamming, and the forwarddrive being broken, then by a reversal of the drive to the apparatus theauger may be removed from the hole by a screwing action.

Furthermore, the rotary drive to the cylinder is through pivotallyadjustable drive means and the cylinder is so mounted that it may betilted forwardly and backwardly, and also sideways, so that even thoughthe machine may be set at an inclination-as on the side of a hill--thepost holes may still be formed vertically. There is also provided an airbreather in the tank which contains the hydraulic fluid required for theoperation of the apparatus.

In order that the invention, and the advantages thereof, may be readilyunderstood and the invention may be conveniently put into practical formwe shall now describe one particular construction of apparatus madeaccording to the invention and also two modifications thereof. Theseconstructions are illustrated in and by .the accompanying drawings,wherein:

Fig. 1 is a view in side elevation showing the post hole digger, madeaccording to the invention, mounted at the rear of a transport vehicle;

Fig. 1A depicts, in side elevation, the reservoir tank for the hydraulicfluid which is employed to raise and lower the auger, and for alteringthe inclination of the auger;

Fig. 2 shows the complete apparatus, in plan view;

Fig. 3 is a view of the apparatus in rear elevation;

Fig. 4 shows a vertical cross-section through the driving apparatus,that is to say the devices for raising and lowering the auger and fordriving it rotationally, the arrows depicting the direction of flow ofhydraulic fluid when the auger is being lowered and the dotted arrowsillustrating the flow of air to the auger;

Fig. 5 illustrates, in vertical cross-section, the prepared constructionof the auger and the means for connecting it to the lower end of thecylinder so as to provide for a supply of air to the lower end portionof the auger when the anger is being withdrawn from the ground;

Fig. 6 is a vertical cross-section taken on the line and in thedirection indicated by the arrows 6-6 of Fig. 5.

Fig. 7 is a horizontal cross-section taken on the line and in thedirection indicated by the arrows '7-7 of Fig. 4;

Fig. 8 shows, in vertical cross-section, a modification of the airsupply to the interior of the auger; and

Fig. 9 illustrates, in vertical cross-section a modified arrangement ofthe cylinder and piston, with the hydraulic feed thereto.

The pipes for the hydraulic system are shown in Fig. 2 only, forpurposes of clarity; and Figs. 4-9, inclusive are shown on larger scalethan Figs. 1, 2 and 3.

As illustrated in the drawings the earth boring ap paratus is mountedupon the rear end part of a transport vehicle 11 which also carries asuitable source of powersuch as an electric motor or an internalcombustion engine 12. Two bearing blocks 13 and frame members 14 arealso securely mounted on the vehicle 11, and the yoke 15 which carriesthe main portion of the earth boring apparatus is supported by a shaft16 journaled in the bearing blocks 13. The yoke '15 is thus mounted soas to enable it to be tilted about a longitudinal axis.

At the rear or outer end of the yoke '15 are two bearings 17 wherein arepivotally mounted two trunnions or pintles 18 fastened to the oppositesides of a gear housing 19. Also secured to this gear housing on itsupper side, is an outer tubular housing 20, and an internally splinedguideway 21 is rotatably mounted within said gear housing. A crown wheel22 is fastened .to said guideway-- suitable bearings being provided tosupport the crown wheel in positionand said crown wheel is driven by apinion gear wheel 23 fastened to the inner end of a driving shaft 24which is journaled in bearings mounted within the pin'tle 18 at one sideof the gear housing 19. A tube 25' having a number of substantiallycircular sp-line members 26 secured to-its outer surface, is slidablyfitted within the splined guideway 21-50 as to be longitudinallyslidable within the outer tubular housing 20, and the lower end of saidtube 25 projects downwardly through the lower side of the gear housing19.

A plug member 27 is fastened to the lower-end of the tube 25. The memberhas a-central boss 28 on its inner, or upper, face, and on its outerfaceis a larger boss '29 to which the auger 30 is fastened. The rotarydrives are such that when the'pinion 23 is rotated the crown wheel 22will be driven, and a drive will be imparted through the internallysplined guideway 21 to the splined tube 25, and thence to the auger 30.

Mounted within the splined tube 25 is an inner tube or cylinder 31having a plate 32 at its upper end. The plate 32, cylinder 31 andsplined tube 25 are securely fastened together so that the cylinder 31will move with the tube 25, and vice versa. At the lower end of thecylinder 31 is a closure plug 33 having in its under surface a recess 34wherein the boss 28 on the inner surface of the plug member 27 isengaged-the cylinder 31 being thus held coaxial with the splined tube25. A tubular piston rod 35 having at its lower end a suitablepistonhead 36 is so mounted that it fits slidably within the cylinder31, passing through the plate 32, and a central pipe or tube 37 isfitted within the tubular piston rod 35 so as to project downwardlythrough the piston head 36 and into the lower end portion of thecylinder. A suitable gland 38 is provided on the plate 32 at the upperend of the cylinder 31, fitting about the piston rod 35 so that leakageof oil between said cylinder 31 and the tubular piston rod 35 will beprevented or at least largely reduced.

The upper end portion of the tubular piston rod 35 is firmly securedwithin an end closure 39 at the upper end of the outer tubular housing20, so that the piston 35 is held in fixed position relative tothat-outer housing. The upper end portion of the tube 37 projectsthrough and is secured to the closure plate 40 at th upper end of thepiston rod 35. Suitable oil pipe lines 41 and 42 are connected to theupper end portion of the tubular piston rod 35 and to the upper endportion of the central pipe or tube 37, respectively.

The piston head 36 consists of a sleeve member 43 which is fastened tothe lower end of the piston rod 35 and to the lower end portion of thecentral tube 37, a piston head member 44 rotatably mounted on saidsleeve 43, glands 45 fitted about said member44, and opposed roller orball races 46 and 47 at the opposite ends of the member 44. The upperhall race 46 is located between .a shoulder on the sleeve member 43 andsaid member 44 and the lower part of the cage of the lower ball race 47is non-rotatable on the sleeve member 43, The piston head member 44 can,therefore, turn rotationally with the cylinder 31. V g

If hydraulic fluid under pressurebe introduced to the through the pipe42 then the direction of flow will be as indicated by the arrows in Fig.4, the hydraulic fluid flowing down the central tube 37 and into thelower portion of the cylinder 31. There will thus be exerted a downwardpressure upon the cylinder and an upward pressure upon the piston head36. The piston head being fixed, the cylinder 31 will, therefore, bemoved downwardly. The hydraulic fluid in the upper portion of thecylinder 31 is permitted to escape by flowing through holes 48 providednear the 'lower end of the piston rod 35-a short distance above thepiston head 36-the hydraulic fluid flowing into the :piston rod 35 andthen upwardly so as to pass into the pipe 41. And if the direction offlow of the hydraulic fluid be reversed then the cy inder 31 Will bemoved upwardly.

Near the upper end of the outer housing 20 there is secured an air inletpipe 49 by means of which air is admitted to the interior of the housing20. Openings 50 are formed through the upper end portion of the splinedtube 25 so as to enable air to flow freely from the housing 20 into-thespace between the inner wall of the tube 25 and the outer surface of thecylinder 31. Air passageways 51 are provided in the plug member 27 andan axial passageway 52 is formed in the auger 30, thereby permitting airto how downwardly through said auger.

The mounting of the auger is illustrated in Fig. 5,

interior of the cylinder 31 v as follows:

The auger 30 is screwed on to the boss 29 at the lower end of the member25 and a shear pin 83 is fitted tightly in registering horizontal holesformed through the auger 30. That is to say, if the normaldirection ofrota- .fitted within .the said hole so as to tion of the auger 30' beclockwise (or right hand) then the threads on the boss 29 and, insidethe top of the auger will be left-handed. And if the auger be so madethat its normal direction of rotation be anti-clockwise (or left-hand)then the screw threads will be right-handed. Consequently, if the augerencounter an obstruction such as would cause overloading of componentsof the apparatus the shear pin 83 will break and the boss 29 at thelower end of the member 25 will be unscrewed from the auger. Then, byreversing the direction of the drive the boss .29 may be screwed backinto the open upper endof the auger 30 and the auger disengaged from theobstruction by a-screwing action.

The centering bit 84 at the lower end of the auger 30 is made as aseparatepart which is fastened to the main portion of the auger by atransverse pin 85. This pin is fitted through opposed holes near thelower end of the auger 30 and it passes through a slot 86 in a neckportion of the centering bit 84. That neck portion fits neatly butslidably within the lower end portion of the auger '30, the lower end ofsaid auger being charnfered inwardly at 87 and the centering bit 84'being shaped accordingly so that when the centering 'bit 84 is pressedupwardly its 'chamfered shoulder will press firmly upon the chamferededge 87, a suitable liquid seal being provided .to seal the-lower end ofthe auger 30 against entry of dirt and grit. The neck portion of thecentering bit 84 has an upward extension 88 formed with a hole extendingdownwardly into the slot 86. This hole is screw threaded at its upperend, to receive a bolt 89 having a lock nut. thereon. A helicalcompression spring 90 is press upon the pin 85. This spring 90 acts tohold the upper portion of the centering bit -84 vertically retractedinto the auger 30. Air passageways 91 are provided in the neck positionof the centering bit so as to enable the free flow of air downwardlytherethrough to an appropriate postion ad- 'jacent the chamfered edge 87at the lower end of the auger.

During the boring action of the auger 30 the centering bit 84 pressesupwardly upon the chamfered edge 87 but when, upon completion of aboring operation, the auger 30 is drawn upwardly for a short distancethe centering bit remains stationary particularly in heavy soil therebyproviding a circumferential opening between the chamfered edge 87 andthe chamfered shoulder of the bit 84. Thelower or outlet ends of thepassageways 91 will then be in registration with that opening so as topermit the free flow of air into the lower end of the hole bored in theearth. The movement of the centering bit 84 relative to the auger 30 islimited by the pin 85 engaging the top of the slot 86.

By reason of this arrangement air may flow through the pipe 49 into thehousing 20 and splined tube 25, thence through the passageways 51 and52, and out through the circumferential opening between the chamferededge 87 and the shoulder 84. When the auger bit 30 is to be withdrawnfrom a formed hole in the earth the air introduced to the lower portionof that hole will relieve any reduction in pressure which may resultfrom the upward movement of the auger and thereby facilitate the removalof the auger from said hole.

The drives to the pinion 23 and the means for moving the gear housing19, and the apparatus supported thereby, in a pivotal manner are ofsomewhat conventional character. For convenience, a brief description isnow given.

A gear box 55 is carried by the yoke 15 and in this gear box is mountedthe gears driving the shaft 24, and also bearings for a shaft 56, whichis connected through a universal to one end of an extensibletransmission member 57. This member 57 consists of two parts, one ofwhich is slidably fitted into the other in such manner that there is adriving connection between them. The other end of the extensible member57 is connected through a universal to the output shaft 58 of the engine12. As the shaft 24 is co-axial with the pintles or trunnions 18supporting the gear box 19 and the auger-operating apparatus, and as thetransmission member 57 is extensible, and that member is connected tothe shafts 56 and 58 through universal joints, the gear housing 19 andthe apparatus carried thereby may be moved pivotally relative to theyoke 15 without the rotary drives being affected. And the yoke 15 may bemoved pivotally on its shaft 16 without affecting the drives to thecrown wheel 22 by reason of the provision of the extensible transmissionmember 57'.

Mounted on the frame members 14 are the devices for moving the gearhousing 19 angularly and the drives for moving the yoke 15 pivotally.

A member 59 is mounted on the shaft 16 so that it will move with saidshaft, and pairs of links 60 and 61 are pivotally mounted on said member59, said links being connected by stays 62. Two links 63 are connectedto the outer housing and to the upper ends of the links 61, the links 63being angled at their front ends and interconnected by a cross-bar 64. Ahydraulic ram 65 is mounted at the upper ends of the links 60 and thepiston of said ram is connected to the cross-bar 64. The parts are soarranged that when the piston of the ram 65 is moved outwardly the outerhousing 20 will be tilted rearwardly in the direction of the arrow A inFig. 1.

The devices for moving the yoke 15, and the apparatus carried thereby,pivotally about the shaft 16 consist of a hydraulic ram 66 which ispivotally mounted on the transport vehicle 11 and having its pistonconnected to a crank arm 67 secured to the yoke shaft 16.

It will be apparent that if the hydraulic ram 66 be operated then theyoke 15, the apparatus carried thereby and also the member 59 whichsupportsthe links, 60,61,

62 and 63 and the ram 65 will be moved pivotally about the shaft 16 asfulcrum. V

The arrangement of the several sets of hydraulic pipes and the controlsfor operating the apparatus are. shown diagrammatically in Fig. 2. .Thepipes 68, 69 which are connected to the hydraulic ram 65 are alsoconnected to a control member 70, the pipes 71, 72 from the hydraulicram 66 are connected to a control member 73 and the pipes 41, 42-fromthe tubular, piston'rod 35 and the central tube respectively areconnected to a control member 74. The three control members areinterconnected by inlet and return headers which have hydraulic pipes 75and 76, respectively, connected to them. Suitable relief valves areprovided. The pipe 75 is connected to a pump 77 driven from the engine12 and a short pipe 78 leads from the pump 77 to a hydraulic fluidreservoir or tank 79. The return pipe 76 is connected directly to thetank 79.

There is also provided a gear shift lever 80 bymeans of which therotational drives to the pinion 23 andcrown wheel 22 may be controlled.

- An important, though simple, feature of the invention isillustratedinfFigs. 1A and 2. This feature consists of the provision of means formaintaining atmospheric pressure on top of the oil in the tank 79, whenthe tank is tilted owing to the machine resting upon uneven and/orsloping ground. For this purpose we provide several tubes 81 secured tothe underside of the top of the tank 79 and extending from the severalcorners of the tank to the filler neck 82. This filler neck extends a'substantial dis tance upwardly from the top of the tank 79, and the endsof the tubes 81 are located only a short distance below the top of thefiller neck 82. Consequently, the tank 79 may be tilted to anyreasonable position and when so tilted one or more of the breather tubes81 will conduct air to the highest portion of the tank 79 so as tomaintain atmospheric pressure above the level of oil in the tank.

Fig. 8 illustrates a modified construction of air supply line leading tothe passageways 51 in the plug 27. Instead of the air being admitted tothe interior of the outer housing 20, and thence to the interior of thetube 25, there are provided one or more hollow tubes 92 on the outerside of the tube 25. These tubes 92 may also act as splines 26 or theymay be provided as independent air supply lines fitting slidably inappropriately shaped recesses in the member 21. Each of the tubes 92 isclosed at its lower end and a short distance above said'lower end thereis an outlet opening communicating with a passageway 51A- in the plugmember 27 so that air is permitted to flow from the tubes 92 into thepassageways. The remainder of the construction is substantially the sameas that already described.

Referring now to the modified construction illustrated in Fig. 9, thereis provided an outer housing 20 fastened to the gear housing 19 aspreviously described. Fastened to the upper end of the outer housing 20is a closure member 39, and securely fastened to that member 39 is acylinder tube 93 which is located within the housing 20 so as to beco-axial therewith. Also secured to the upper end of the housing is anoil supply tube 37A which fits coaxially through the housing and thecylinder tubethe oil supply tube 37A extending downwardly through thecylinder tube 93 to within a short distance of the bottom of saidcylinder tube.

Slidably fitted in the driving member 21 is an externally splined tube25A adapted to have the auger bit 30 detachably fastened to its lowerend in the manner as previously described. This splined tube can extendup wardly into the outer housing 20, fitting between the inner wall ofthat housing and the outer wall of the cylinder tube 93 which is fixedlymounted within the housing 20. Within the'splined tube 25A, near thelower end thereof, is fastened the lower half of thrust ball or rollerrace .94

and :the upper :part. of :that hearing is fastened to the lower end of atubular piston rod 95,,a member 96 being provided :to'. hold. togetherthe two parts of. the race 94. The lower end of the tubular pistonrod'95 is closed, the piston rod being of such diameter internally that-it fits. about the oil supply tube 37A and of such external diameterthat it fits freely within the fixed-cylinder tube 93.

A piston head '97 is fastened to the upper end of the piston rod 95,said-piston head-97 having a suitable gland 98 to prevent leakage of'oil pastthe oil supply tube 37A and a gland99 to prevent leakageofi oilpast the wall of the cylinder tube '93. A short distance below thepiston head 97 openings lttllaareprovided in the wall of the tubularpiston -rod95. At the bottom end of the-cylindter tube 93 there isfastened a member 101 having "a suitable gland 102 fitting about thepiston rod 95 in such manner that leakages of fluid .past the gland are--substantially :prevented. Also fitted to the closure;39at-tlie topoftheouter housing 20 is a second oil supply tube 41 which communicatesdirectly with the upperendof the cylinder tube 93 supplying hydraulicfluid to the interior of said cylinder tube 'above the piston head 97.

It is robe-noted that'in this construction theouter hous- 'ing 20,cylinder tube 93 and central tube 37A are stationary parts and thesplined tube 25A and tubular piston rod 95 are movable relative tosaidstationary parts.

' The arrangement of the parts is such that hydraulic fluid suppliedthrough the central tube 37 A will flow downwardly through that tubeandout the lower end thereof into the interior of the tubular'piston rod95. The fluid canthen flowthrough the openings 100 into the stationarycylinder tube 93. The hydraulic fluid will then exert pressure betweenthe member 101 and the underside of the piston head 97. As .the member101 is held in fixed position the upward pressure on the underside ofthe piston head will operate in such a manner as to cause the pistonhead 97, as well as the tubular piston rod 95, the thrust bearing 94,and the splined tube 25A to rise relative to the cylinder tube 93.Hydraulic fluid above the piston head 97 can flow freely through thereturn pipe 41.

7 If the direction of flow of hydraulic fluid be reversed then the fluidwill flow through the pipe 41into the upper 'end portion of the cylindertube 93 and will force the piston head 97, tubular piston rod 95, andsplined tube 25A downwardly relative to the cylinder tube 93. Thehydraulic fluid within the lower portion of the cylinder tube will thenbe forced to flow through the openings 100 into the tubular piston rodand thence through the open lower end of the central tube 37A so as tobe exhausted through said tube.

The rotary motion imparted by thepinion gear wheel 23 acting through thecrown gear wheel 22 and the member 21 will-cause to be rotated thesplined tube 25A, and the auger 30mounted at its lower end, but will notcause the tubular piston rod 95 to rotate. Consequently, the glands 98,99 and 102 are exposed to axial reciprocating movement only, and not torotational action. The air supply system previously describedin eitherof its formsmay be readily incorporated with this construction ofapparatus, as may be the other features described above. As shown inFig. 9, air holes 51X may provide for passage of the air to the auger.

What wedo claim is:

1. In a post hole digger the combination of a driving member mounted forrotational motion comprising a hollow cylindrical tube, a single crownwheel surrounding and firmly joined to said tube, said tube containingvertical splined guideways on its inner surface, a driven member-oftubularshape having spline members on its outersurface mounted slidablywithin said driving member and operatively connected thereto so that thedriven member adapted to rotate when the drivingmember is rotated,threaded means for mounting at one end ot the driven member an angerhaving thereon aheliea'l fiight, a piston mounted in the driven member,means for supplying fluid under pressure selectively to either side ofthe piston, means for sealing the end of the driven member adjacent tothe auger against ingress of foreign matter to its interior, the drivenmember being adapted to move linearly in one direction when .fluid underpressure is supplied to one side of the piston and to move linearly inthe opposite direction when fluid under pressure is supplied to theother side of the piston, and means contained within said driven memberfor supplying air from the upper-end to the lower end of said drivenmemher, an anger atone end of the driven member, means for supplying airfrom the lower end of said driven member to the upper end-of the auger,and an air passage in the anger, the outlet of the air passage beinglocated below the lower end 'of the auger flight.

2. In a post hole digger the combination of a driving member mounted forrotational motion comprising a hollow cylindrical tube, a single crownwheel surrounding and firmly joined to said tube, said tube containingvertical splined guideways on its inner surface, a driven member#oftubular shape having spline members on its outer surface mountedslidably within said driving member and operatively connected thereto sothat the driven member is adapted to rotate when the drivingmember isrotated, threaded means for mounting an auger at one end of the drivenmember, a'piston mounted in the driven member, means for supplying fluidunder pressure selectively to either side of the piston, means forsealing the end of the driven member'adjacent to the auger againstingress of foreign matter to its interior, the driven memher beingadapted to move linearly in'one direction when fluid under pressure issupplied to one side of the piston and to move linearly in the oppositedirection when fluid under pressure is supplied to the other side of thepiston, and means contained within said driven member for supplying airfrom the upper end to the lower end of said driven member, an angerprovided with screw threads engaged with screw threads formed at thelower end of said driven member, and a shear pin extending through thelower end of said driven member and the upper end of said auger, thescrew threads of the driven member and of the auger being firmly engagedto prevent longitudinal movement and being opposite in hand to thenormal operative direction of rotation of the auger.

3. In a post hole digger, a driving member mounted for rotational motioncomprising a hollow cylindrical tube, a single crown wheel surroundingand firmly joined to said tube, said tube containing vertical splinedguideways on its inner surface, a driven member of tubular shape havingspline members on its outer surface mounted slidably within said drivingmember and operatively connected thereto, the driven member beingadapted to rotate when the driving member is rotated and the drivenmember being adapted to have an auger threadedly fastened to one end ofsaid driven member, a cylinder within the driven member, a piston 'headwithin the cylinder, a piston rod connected to the piston head, meansfor supplying hydraulic fluid under pressure to one end portion of thecylinder, means for supplying hydraulic fluid under pressure to theopposite end portion of the cylinder, the driven member being adapted tomove linearly in one direction when hydraulic fluid under pressure isfed into one. end portion of the cylinder and to move linearly in theopposite direction when hydraulic fluid under pressure is. fed into theother opposite end portion of the cylinder, and passageways containedwithin said driven member for supplying air from the upper end to thelower end of said driven member, an auger connected to the drivenmember, said auger having an air passage from its upper end which is incommunication with the lower end of -the air passageway of-the drivenmember to an outlet below the lower end of the auger flight, and a valvein the air passage, said valve being adapted to seal the outlet of theair passage against ingress of dirt and grit.

4. In a post hole digger, a driving member mounted for rotational motioncomprising a hollow cylindrical tube, a single crown wheel surroundingand firmly joined to said tube, said tube containing vertical splinedguideways on its inner surface, a driven member of tubular shape havingspline members on its outer surface mounted slidably within said drivingmember and operatively connected thereto, the driven member beingadapted to rotate when the driving member is rotated and the drivenmember being adapted to have an auger threadedly fastened to one end ofsaid driven member, a cylinder within the driven member, a piston headwithin the cylinder, a piston rod connected to the piston head, meansfor supplying hydraulic fluid under pressure to one end portion of thecylinder, means for supplying hydraulic fluid under pressure to theopposite end portion of the cylinder, the driven member being adapted tomove linearly in one direction when hydraulic fluid under pressure isfed into one end portion of the cylinder and to move linearly in theopposite direction when hydraulic fluid under pressure is fed into theother opposite end portion of the cylinder, and passageways containedwithin said driven member for supplying air from the upper end to thelower end of said driven member, an air inlet opening at the upper endof said driven member, said cylinder within said driven member beingspaced from the inner surface of said driven member so as to provide anair passageway from the top of the driven member to the lower endthereof.

5. In a post hole digger, a driving member mounted for rotational motioncomprising a hollow cylindrical tube, a single crown wheel surroundingand firmly joined to said tube, said tube containing vertical splinedguideways on its inner surface, a driven member of tubular shape havingspline members on its outer surface mounted slidably within said drivingmember and operatively connected thereto, the driven member beingadapted to retate when the driving member is rotated and the drivenmember being adapted to have an auger threadedly fastened to one end ofsaid driven member, a cylinder within the driven member, a piston headwithin the cylinder, a piston rod connected to the piston head, meansfor supplying hydraulic fluid under pressure to one end portion of thecylinder, means for supplying hydraulic fluid under pressure to theopposite end portion of the cylinder, the driven member being adapted tomove linearly in one direction when hydraulic fluid under pressure isfed into one end portion of the cylinder and to move linearly in theopposite direction when hydraulic fluid under pressure is fed into theother opposite end portion of the cylinder, and passageways containedwithin said driven member for supplying air from the upper end to thelower end of said driven member, at least one air passageway memberbeing secured to the outer surface of the driven member to constitute aspline for making a driving connection between the driving and drivenmembers.

6. In a post hole digger, the combination of a driving member mountedfor rotational motion about a generally vertical axis, a tubular drivenmember extending generally vertically through said driving member andaxially slidably keyed thereto for rotation therewith and for axialreciprocation with respect thereto, said driven member being adapted tomount an auger at the lower end thereof, a piston and cylinderassemblage, of which one of the piston and cylinder elements is axiallyfixedly mounted and the other is rigidly connected to said driven memberfor axial reciprocation of the latter under the influence of fluid underpressure acting alternately on opposite sides of said piston element, apacking between said piston and cylinder elements, bearing means betweensaid driven member and said assemblage effective to permit rotationalmotion of said driven member by said driving member withoutcorresponding relative rotational motion of said piston and cylinderelements and said packing therebetween, an auger mounted on the lowerend of said driven member, and a passageway contained within said drivenmember for supplying air from the upper end to the lower end of saiddriven member.

7. The post hole digger of claim 6 wherein said piston has a piston rodconnected to said driven member through said bearing means, and whereinsaid driven member laterally encloses said piston rod to protect thelatter from dirt handled by an auger secured to the lower end of saiddriven member.

8. The post hole digger of claim 6 wherein said piston has a piston rodon which said piston is journalled by said bearing means, and whereinsaid driven member is a part of said cylinder whereby rotational motionof said driven member and cylinder imparts corresponding rotationalmotion to said piston and said packing.

9. In a post hole digger, the combination of a driving member mountedfor rotational motion about a generally vertical axis, a driven memberextending generally vertically through said driving member and axiallyslidably keyed thereto for rotation therewith and for axialreciprocation with respect thereto, an anger having a helical flighttherearound, said auger being threadedly engaged with the lower end ofsaid driven member, the threads of said auger and of said driven memberbeing of hand opposite to that of the flight, and complementary keymeans holding said auger and said driven member against relativerotation whereby torque is transmitted by said driven member to saidauger for digging a hole as said driven member and auger are moveddownwardly and rotated, said threads being effective, upon failure ofsaid key means, to permit continued rotational motion of said drivenmember without corresponding rotational motion of said auger and toenable positive withdrawal of said auger from a hole by reverserotational motion of said driven member.

References Cited in the file of this patent UNITED STATES PATENTS168,454 Coman Oct. 5, 1875 1,811,002 Dodds June 23, 1931 2,192,192Johansen Mar. 5, 1940 2,320,612 Kandle Jan. 1, 1943 2,415,572 JaquesFeb. 11, 1947 2,565,547 Collins Aug. 28, 1951 2,598,203 Acker May 27,1952 FOREIGN PATENTS 144,262 Australia Nov. 19, 1951

